In 2009, a simple software bug in the Toyota Prius caused a massive problem. The issue was a malfunction in the braking system where the brakes would suddenly become unresponsive.

The bug occurred in the software that controlled the anti-lock braking system. It is a safety feature designed to prevent the wheels from locking during hard braking, allowing the driver to maintain steering control. In this case, the software misinterpreted sensor readings from the wheels and the road surface, causing the braking system to behave incorrectly, leading to delayed or insufficient braking.

When drivers reported that their brakes were acting strangely, Toyota discovered that the software in the electronic control unit, which governs the braking system was incorrectly processing the sensor inputs. This led the system to apply the brakes incorrectly during certain conditions, such as when the road was wet or the car was slowing down rapidly.

Toyota had to recall 800,000 Prius cars worldwide and reprogram the affected software to fix the issue. The recall not only cost the company over $1 billion, but also hurt their reputation as a trusted brand known for safety and quality.

This incident highlights even a small error in crucial systems can lead to huge financial losses and safety issues, and how important it is to carefully test software before deploying them in real-world applications.